Reinforced



M r 1954 s. s KISTLER ETAL 3,123,948

REINFORCED GRINDING WHEEL AND REINFORCING STRUCTURE THEREFOR Filed Oct. 4, 1962 2 Sheets-Sheet l INVENTORS.

6 7772167 6' fink-2 1 7 March 1964 s. s. KISTLER ETAL 3,123,948

REINFORCED GRINDING WHEEL AND Filed Oct. 4, 1962 REINFORCING STRUCTURE THEREFOR 2 Sheets-Sheet 2 INVENT Rs. 547712107 61 A1752 6' 7" United States Patent 3,123,948 REINFORCED GRINDING WHEEL AND REHJ- FORCING STRUCTURE THEREFOR Samuel S. Kistler, Salt Lake City, Utah, and Charles V.

Rue, Tiflin, Qhio, assignors to Wakefield Corporation,

Detroit, Mich, a corporation of Michigan Filed Dot. 4, H62, Ser. No. 228,435 11 Claims. (Cl. 51-2tl4) The present invention broadly pertains to reinforced abrasive articles and more particularly to improved abrasive articles such as grinding Wheels and the like incorporating therein a unique fiberglass reinforcing network of a prescribed geometrical configuration and to the method of making reinforced abrasive articles and the reinforcing network. The present application comprises a continuation-in-part of our prior co-pending United States patent application Serial Number 78,171, filed December 23, 1960, and now abandoned.

Comparatively large grinding wheels of the resinoid bonded type are in a widespread use in industry for snagging steel and other metals. These relatively large grinding wheels are generally used without any coolant and are rotated at relatively high speeds. The abusive operating conditions to which these grinding wheels are subjected frequently cause the development of radial cracks in the wheels extending inwardly from the periphery thereof which materially reduce the strength of the wheels creating a serious safety hazard to the operating personnel in the vicinity and to the machine itself in the event of breaking or disintegration of the grinding wheels. For this reason, it is customary to discard a grinding wheel as soon as radial cracks are observed therein. In spite of this precaution, however, a grinding wheel does occasionally break sometimes causing serious injury to an operator in spite of the safety measures incorporated in the machine.

To reduce the tendency of high speed grinding wheels to disintegrate, a variety of reinforcing techniques have heretofore been employed or proposed to strengthen the abrasive structure against centrifugal forces. These techniques include embedding metallic rings and fabrics of various compositions in the grinding wheel during the forming process thereof which are intended to reinforce and prevent disintegration of the grinding wheel. Almost invariably the reinforcing elements in the grinding wheel are spaced a substantial distance from the peripheral surface thereof to prevent exposure of the reinforcement at the grinding surface so as not to interfere with the grinding action as the wheel decreases in diameter due to wear through continuous use. While some strengthening of grinding wheels has been achieved as a result of incorporating these reinforcing elements, grinding wheel failures still occur as a result of radial cracks forming and moving inwardly from the periphery of the wheel to a point adjacent to the outermost extension of the re inforcing elements. It has now been found that these radial cracks are deflected on reaching the outer point of the reinforcing members and tangentially follow the reinforcing element eventually permitting the outer unreinforced portions of the grinding wheel to fly off. Attempts have also been made to strengthen grinding wheels by incorporating loose fibrous materials such as asbestos, glass fiber, cotton, hemp, and like in random orientation throughout the abrasive structure with no material success.

Based on the successful practice employed in the manufacture of relatively thin grinding wheels of the cutoff type in which alternate layers of abrasive material and fiberglass cloth have been employed to prevent breakage from centrifugal force and accidental impact, relatively large grinding wheels were made employing alternate 3,123,948 Patented Mar. 10, 1964 layers of abrasive material and fiberglass cloth. It was found, however, that the quantity of fiberglass cloth required to achieve a substantial increase in the strength of the grinding wheel was extremely high resulting in a serious impairment of the grinding efficiency of the wheel and concurrently increasing the cost of the wheel to a commercially prohibitive level. In addition, the grinding wheels made were of a laminar structure and the stress gradients in the wheel caused separation of adjacent layers resulting in eventual disintegration of the unsupported abrasive layers.

There has been accordingly a heretofore unfilled need for a reinforcing network for objects adapted to rotate at relatively high speeds and particularly for relatively large grinding wheels, which network not only substantially increases the strength of the grinding wheel to prevent disintegration thereof but additionally does not detract from the grinding efficiency nor increase the cost thereof to a commercially prohibitive figure. Moreover, there has been a continuing problem of manufacturing abrasive articles incorporating fiberglass reinforcing elements therein whereby the surfaces of the glass fibers are not damaged by the abrasive particles during the forming operation of the abrasive article thereby not impairing the strength of the reinforcing elements.

It is accordingly a primary object of the present invention to provide a unique fiberglass reinforcing network and method of making the same which, when imbedded in abrasive particles, substantially increases the strength thereof beyond that heretofore obtainable with similar quantities of reinforcement.

Another object of the present invention is to provide an improved reinforcing network having a geometrical configuration of reinforcing elements which provides maximum resistance to disintegration of rotating articles in which the network is imbedded and particularly snagging grinding wheels and the like whereby optimum reinforcement is achieved in lieu of the random and haphazard reinforcing techniques heretofore employed wherein only a fragment of the reinforcing benefits were obtained.

Still another object of the present invention is to provide a method for making reinforcing networks in any one of a variety of or combination of desired configurations and in which form the reinforcing network can readily be incorporated in an abrasive article.

Yet still another object of the present invention is to provide an improved fiberglass reinforcing network having a geometrical pattern that extends to a point contiguous to the periphery of the grinding wheel thereby reinforcing the outer portions thereof and that does not detract from the grinding efficiency of the wheel as the diameter thereof decreases exposing the projecting portions of the reinforcing network.

A further object of the present invention is to provide a method of forming abrasive articles incorporating fiberglass reinforcing elements therein whereby the surfaces of the fiberglass reinforcing member are not scratched or otherwise damaged by the abrasive particles during the forming process so that the strength of the reinforcing network is not impaired.

A still further object of the present invention is to provide improved reinforced abrasive articles such as grinding wheels and the like incorporating therein a reinforcing network and which articles are of high strength, safe operation, excellent durability, excellent grinding efficiency, and of economical manufacture.

Still another object of the present invention is to provide a method for making rotatable abrasive articles such as grinding wheels and the like incorporating therein a fiberglass reinforcing network and which method is of simple and economical control and operation producing abrasive articles which are of high strength and of high grinding efficiency.

The foregoing objects and advantages of the present invention are based on the discovery that substantially superior reinforcing characteristics are achieved by employing reinforcing networks having a nonuniform configuration and distribution of the reinforcing elements thereof in comparison to that heretofore obtainable by employing random oriented reinforcing structures or substantially uniform reinforcing structures such as woven fabrics and the like. The nonuniform reinforcing network comprising the present invention comprises a continuous fiberglass cord or cable consisting of a plurality of continuous fiberglass filaments and which is disposed in a cuspate geometrical pattern wherein chords are formed of which a predominating quantity thereof pass through a chordal region lying between the hole or arbor in the article and a circle whose radius is equal to the radius of the hole or arbor plus about one-third of the distance from the hole or arbor to the periphery of the article. The cusps of the network extend at least about two-thirds of the radial distance from the hole or arbor to the periphery of the article providing therewith a resultant reinforcing network having the optimum configuration. In the preferred practice of the present invention the reinforcing network is preliminarily rigidified by a suitable resinous bonding agent and imbedded in a mold containing abrasive articles which are thereafter bonded together without the use of high pressures forming therewith a high strength resinoid bonded abrasive article containing a relatively small proportion but highly effective reinforcing network.

Other objects and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, wherein:

FIGURE 1 is a perspective exploded view of a typical reinforcing network comprising two reinforcing members interconnected by a continuous cable or cord comprising a plurality of continuous glass filaments;

FIGURE 2 is a plan view of the uppermost tier of the reinforcing network illustrated in FIGURE 1;

FIGURE 3 is a plan view of another typical cuspate geometrical pattern of a reinforcing member using a smaller number of cusps than that shown in FIGURE 2;

FIGURE 4 is a diagrammatic plan view of a modified form of the reinforcing network of FIGURE 2 which comprises one cuspate pattern of the type shown in FIG- URE 2 and two patterns of the type shown in FIGURE 3 interconnected so as to form a single network and radially centered in an abrasive wheel shown in phantom;

FIG. 5 is a diagrammatic plan view of still another alternate satisfactory cuspate geometrical pattern for a reinforcing member illustrating a smaller internal diameter arrangement;

FIG. 6 is a fragmentary perspective view partly in section illustrating a typical structure of the continuous fiberglass cord or cable;

FIG. 6A is a fragmentary perspective view partly in section illustrating a preferred form of the continuous fiberglass cord;

FIG. 7 is a transverse vertical sectional view through a vacuum mold assembly for making reinforced abrasive articles in accordance with the preferred practice of the present invention and illustrating the disposition of a reinforcing network therein;

FIG. 8 is a transverse vertical sectional view of the vacuum mold assembly similar to that shown in FIG. 7 but showing the abrasive grains, reinforcing network, and bond mix in position before application of vacuum;

FIG. 9 is a plan view of a typical forming jig incorporating a plurality of pins thereon which is employed for making the reinforcing network of a desired cuspate geometrical pattern; and

FIG. 10 is a side elevation view of the forming jig shown in FIG. 9 and illustrating the manner in which a plu- .4 rality of tiers or layers of the reinforcing network are constructed. N

The improved reinforcing characteristics of the reinforcing network comprising the present invention are predicated on the unique configuration and nonuniform distribution of the reinforcing elements comprising the reinforcing network. The configuration of the reinforcing network and the distribution of the reinforcing elements thereof, can vary within prescribed limits in accordance with the dimensions, structure, strength, and operating conditions of the rotating article in which it is imbedded. The optimum configuration and distribution of the reinforcing network for a specific rotating article such as an abrasive grinding wheel and the like, can be derived by a mathematical stress analysis approach in which combined considerations are made of the stress gradients present in bodies rotating at high speeds, stress concentrations adjacent to imbeddcd reinforcing materials, and the grinding efficiency and wear rate of the wheel as affected by the quantity of the reinforcing material used and the disposition thereof in the grinding wheel. In this manner the configuration and disposition of the reinforcing network and the quantity employed can be optimized to assure proper strength of the abrasive article and minimize the displacement of the abrasive grains with reinforcement whereby optimum grinding efficiency and economy are achieved.

Resinoid bonded grinding wheels of the general type used for snagging steel and foundry castings employing any one or a mixture of conventional abrasive particles and bonding agents therein have a density usually of about 3 grams per cubic centimeter and a modulus of elasticity of about 2,000,000 p.s.i. The fiberglass cord or cable employed in the reinforcing member comprising the present invention which consists of a plurality of intertwined plys or rovings each of which in turn is comprised of a plurality of strands made up of a plurality of fine sized continuous fiberglass filaments is of extremely high tensile strength and has a modulus of elasticity in excess of that of the grinding or abrasive material. A modulus of elasticity of about 10,000,000 p.s.i. for glass is accepted which is about five times greater than that of the abrasive material. Accordingly, strains developed in the abrasive article during rapid rotation as a result of centrifugal forces will develop about five times the stress in the fiberglass reinforcing members as in the abrasive Wheel structure, or in other words, for a unit strain, a stress five times as great is required to cause the same strain in the reinforcing member as in the abrasive structure of the wheel. Due to the integral bonding between the abrasive wheel structure and the reinforcing member imbedded therein the relative strain between the abrasive structural material and the fiberglass reinforcing member will be the same. For example, a stress in the abrasive grinding wheel structure of about 6,000 p.s.i. which corresponds to about the ultimate strength of the abrasive material will be paralleled by a stress in the fiberglass reinforcing member of about 30,000 p.s.i. As a result, the fiberglass reinforcing member makes a material contribution to the strength of the grinding wheel.

It has been shown that time sized individual glass fibers having a diameter of about 0.0002 inch have a tensile strength of about 450,000 p.s.i. Fiberglass cables or cords made of these continuous glass filaments also have extremely high tensile strength ranging from about 200,000 p.s.i. to about 450,000 p.s.i., or for a conservative value, a tensile strength of about 200,000 p.s.i. Accordingly, a fiberglass reinforcing member having a cross sectional area of less than about M; of a square inch would suifice to withstand the stress of 30,000 p.s.i. under the loading condition set forth in the preceding paragraph.

It can also be shown mathematically that the stresses imposed on a grinding wheel through centrifugal forcesincreases progressively on moving in a radial directionfrom the periphery toward the center of the wheel,

This can be shown mathematically by calculating the force acting on each segment of the wheel bounded by two radii extending out from the center of the wheel and disposed one inch apart at the peripheral surface thereof. The force acting on each segment can be calculated by using the following equation:

F :the force in pounds b=the width of the wheel in inches d :the specific gravity of the wheel V=the peripheral speed of the wheel in feet per minute,

and

a=the ratio of the radius of the internal hole in the wheel to the radius of the periphery of the wheel.

For a typical snagging abrasive wheel having an external diameter of 24 inches, an internal hole or arbor having a diameter of 12 inches, a thickness or width of 3 inches, a specific gravity of 3, and rotating at a surface speed of 12,000 feet per minute, an outward force (F) of about 1,418 pounds is exerted on each segment of the wheel. The unique configuration of the reinforcing network comprising the present invention provides progressive distribution of the quantity of reinforcing material consistent with the radial stress (force per unit area) which increases toward the center of the wheel.

As will be noted in the drawings, the reinforcing members comprising the present invention have geometrical configurations predicated on a nonuniform distribution of the fiberglass cable consistent with the stress gradient in the wheel. As will be noted in FIGURES 1 through 5, the pattern is of a so-called cuspate geometrical configuration including an inner chordal region com prised of a plurality of intersecting chord segments and disposed concentric to the center of the grinding wheel. This so-called chordal region represents an area of maximum concentration of the fiberglass cable and is adapted to be disposed at the inner portion of the grinding wheel adjacent to the inner hole or arbor therethrough at which the maximum stress concentration exists. As the length of the chord segments defining the inner chordal region of the reinforcing member decrease in length and in the illustrations given where these chord segments are tangent to a chordal circle the chordal circle approaches a true ring and can be treated for the purposes of the following calculations as a continuous loop or ring disposed concentrically in the grinding wheel in a manner similar to that heretofore employed in strengthening grinding wheels of the general type herein described in which rings of steel, for example, were employed.

The cross sectional area of the so-called inner chordal ring or plurality of rings formed by the chords of the reinforcing members required to withstand the tensile stress can be calculated in accordance with the following equation:

F=1.25A' bdr V (1a wherein:

r=the outside radius of the wheel in inches, and the remaining symbols are dimensionally identical to those of the preceding equation.

The foregoing formula is readily derived for calculating the tensile force exerted by the wheel on the inner fiberglass chordal ring to hold the wheel together ignoring the contributing strength of the abrasive structure of the wheel. A grinding wheel of the dimensions, and composition as set forth above and designed to withstand a rotative speed of at least 12,000 surface feet per minute (s.f.p.m.) requires a ring having the ability to withstand a tangential force of about 17,000 pounds. As hereinbefore set forth, the fiberglass cable employed in the reinforcing members has a conservative tensile strength of about 200,000 p.s.i. The cross sectional area of the 6 chordal ring or rings necessary to withstand the tensile force would be about 0.085 square inch.

In addition to the foregoing, it has been shown that the forces acting on the grinding wheel when rotated at high speeds are not purely in a radial direction but include a tangential component as a result of the hoop stress created through the centrifugal forces acting on the wheel. Because of these hoop stresses the stress pattern across a radius of a wheel are a combination of radial stresses and tangential stresses with the resultant stress becoming more tangential during radial movement from the internal reinforcement ring outwardly toward the periphery of the wheel. The stresses in the chordal circle are tangential. Immediately outside this circle the stresses are mainly radial whereas at the surface of the outer periphery of the wheel the stress is essentially a tangential one. In view of this, optimum reinforcement is achieved by novel configuration of the reinforcing network comprising the present invention wherein the continuous fiberglass chords are disposed at an angle to the radii of the grinding wheel thereby providing reinforcement in both tangential and radial directions. Moreover, the major portion of the chord elements of the reinforcing member beyond the chordal region are disposed at an intersecting angle of less than to the radii of the grinding wheel so as to minimize interference with the grinding efficiency at the surface of the grinding wheel as the diameter of the wheel decreases due to wear exposing the outer portions of the reinforcing network imbed ded therein.

In accordance with the foregoing analyses of the dis tribution of stresses in a rotating wheel such as an abrasive grinding wheel and the like, the configuration and nonuniform distribution of the reinforcing elements of the reinforcing network can be optimized for any specific wheel and the operating conditions to which it is to be subjected. A distribution of the reinforcing network wherein the volume or weight of the elements thereof per unit volume of wheel increases in the direction from the outer periphery of the wheel toward the center of the Wheel is achieved in the so-called cuspate geometrical patterns of the reinforcing networks illustrated in FIGURES 1 through 5. The cuspate geometrical pattern suitable for reinforcing networks in accordance with the practice of the present invention can broadly be defined as those wherein a plurality of chords are disposed in an annular region defined by an inner cylindrical surface or circle and an outer cylindrical surface or circle disposed in concentric axial alignment to each other. The inner cylindrical surface or circle generally corresponds to the periphery of the hole or arbor through an article in which the reinforcing network is imbedded and the outer cylindrical surface or circle has a diameter ranging from the periphery of the article to a diameter corresponding to two-thirds of the radial depth of the article. The radial depth of the article is defined as the radial distance between the hole or arbor through the article to the periphery of the article. Each of the plurality of radially projecting cusps is formed by a pair of chord elements which lie in the annular region between the outer cylindrical surface or circle and the inner cylin drical surface or circle. To achieve the mam'mum benefits of this invention, it is preferred that at least about half of the chord elements of the reinforcing network pass through the chordal region. The chordal region is defined as that region disposed between the inner cylindrical surface or circle and an intemediate cylindrical surface or circle concentric thereto and having a diameter which preferably ranges from that of the inner cylindrical surface or circle to a diameter encompassing about one-third the radial depth of the annular region. By this arrangement, the chordal region formed by the chord segments disposed within the intermediate cylindrical surface will generally be disposed within the clamping flanges employed to rotatably mount the wheel and overlying the side surfaces thereof. In addition, the major portion of the chords disposed outwardly of the chordal region are disposed at an angularity of less than 90 to any radii of the wheel so that they will not be tangent to the periphery of the wheel and will not interfere with the grinding action thereof as the diameter of the wheel decreases through use. The only points existing in the reinforcing network having a cuspate geometrical pattern beyond the chordal region which are tangent to the periphery of the wheel exist at the apexes of the cusps wherein the reinforcing elements interconnect the ends of adjacent chords.

A series of substantially regular and planar cuspate geometrical patterns are illustrated in FIGURES 1 through which can be satisfactorily employed in the practice of the present invention and are not intended to be limiting. A reinforcing member 12 is shown in FIG. 2 comprising a continuous fiberglass cord or cable 14 disposed in a cuspate geometrical pattern comprising a plurality of chord elements 16 which generate a plurality of cusps having the apexes or tips 18 thereof lying on an imaginary outer cylindrical surface or circle indicated in dotted lines. It is not necessary that all of the apexes 18 he on the imaginary circle 26, but some can be disposed inwardly therefrom to a point preferably not greater than one-third the radial depth of the wheel. The chord elements 16 intersect each other in overlying relationship and are disposed tangent to an inner cylindrical surface or circle 21 indicated in dotted lines which lies within the chordal region whereby the chordal segments 22 thereof define an inner chordal circle or ring 24 concentric with the outer circle 29. In the specific cuspate geometrical configuration shown in FIG. 2, the apexes 18 of the reinforcing member 12 of adjacent cusps are disposed at an angularity of 22% and the chord elements 16 extend between two points on the outer circle 20 intersecting an arc of 112 /2 A variation in the cuspate geometrical pattern is illustrated in FIG. 3 for a reinforcing member 12a comprised of a continuous fiberglass cable 14 disposed in a plurality of chord elements 16 forming therewith a plurality of cusps having their apexes 18 disposed on an outer circle 20 in a manner similar to that of the reinforcing member 12 shown in FIG. 2. In the specific configuration shown in FIG. 3 the apexes 18 of adjacent cusps are disposed at an angularity of 45 and the chord elements 16 intersect an arcuate segment of the outer circle 20 of 135". It will be noted in FIG. 3 that fewer chordal segments 22 are generated which are disposed tangent to an inner circle 21 in the chordal region defining therewith a chordal circle or ring 24a having a diameter smaller than that of the chordal circle 24 shown in FIG. 2.

Still another variation of the cuspate geometrical pattern is illustrated diagrammatically in FIG. 5 wherein the apexes 18 lying on the outer imaginary circle 20 of adjacent cusps are disposed at an angularity of 22 /2 similar to the pattern shown in FIG. 2 but the chord elements 16 intersect an arc of the outer circle 20 of an angularity of 157 /2 instead of 112 /2 By this arrangement the inner chordal circle 24b formed by the chordal segments 22b is of a reduced diameter from the chordal circles 24, 24a, shown in FIGS. 2 and 3, respectively.

As hereinbefore set forth, the inner chordal region is intended to be disposed adjacent to the internal bore through the abrasive article at the point near the highest stress. It will be apparent from the cuspate geometrical configuration shown that the size of the chordal region can be varied in accordance with the internal bore through the grinding wheel to achieve the desired stress reinforcement. Best reinforcing results have been obtained in the practice of the present invention when a substantial fraction of the chord elements of the reinforcing network pass through the chordal region, or in the cases of the illustrative figures are tangent to the inner circle 21. The preferred chordal region comprises the annular region ranging from the inner circle 21 outwardly to a point spaced a distance of about one-third the radial depth of the wheel as established by the difference between the radius of the internal bore subtracted from the radius of the periphery of the wheel. Best reinforcing characteristics of the outer portion of the grinding wheel beyond the chordal region have been achieved wherein the apexes of the cusps extend at least of the radial distance of the wheel to a point contiguous to the periphery thereof. In each of the cuspate geometrical patterns shown the quantity or volume of the fiberglass cable 14 per unit volume of Wheel progressively increases in the direction from the periphery of the wheel toward the chordal region.

The cuspate geometrical pattern, examples of which are illustrated in FIGS. 2, 3, and 5, can be employed individually, in multiples, or in a variety of combinations to form a reinforcing network 26 as shown in FIG. 4 to achieve the desired reinforcing characteristics of a particular abrasive article. The reinforcing network 26 diagrammatically shown in FIG. 4 is comprised of one reinforcing member 12 having a configuration shown in FIG. 2 and two reinforcing members 12a having a configuration as shown in FIG. 3 which are disposed in overlying relationship and dispos d in concentric relationship in an abrasive wheel 28 indicated in phantom in FIG. 4. The apexes 18 of the combined reinforcing network 26 project outwardly to a point adjacent to the periphery 30 of the abrasive wheel 28. The chordal region of the reinforcing network 26 is disposed concentrically about an internal bore 32 as shown in phantom in the drawings. In reinforcing networks wherein a plurality of reinforcing members are employed, it is preferred that the reinforcing members are interconnected such as by an interconnecting segment or chord 34 as shown in FIG. 1 whereby the entire reinforcing network consists of a continuous fiberglass cable, but that is not necessary to achieve the objectives of this invention.

It will be appreciated by those skilled in the art that within the parameters as hereinbefore set forth, a large number of additional cuspate geometrical patterns can be employed differing from those shown in the drawings which also provide a satisfactory reinforcing network. In addition to the substantially regular and planar patterns illustrated in the drawings, irregular cuspate patterns can also be employed wherein the apexes or tips 18 do not all necessarily lie on the outer cylindrical surface or circle 20 as shown in the drawings. For example, the radial projecting distance of successive cusps could be varied providing therewith an irregular cuspate pattern wherein about half of the chords pass through the inner chordal region. In addition, the chord elements 16 comprising the cuspate geometrical pattern need not be disposed in substantially the same plane whereby the apexes or tips 18 of the cusps formed are axially spaced from each other forming therewith a reinforcing member having a depth of any desired magnitude. In such event at least about half of the chord elements preferably pass through the inner chordal region.

The fiberglass cord or cable 14 from which the reinforcing members are constructed can comprise a plurality of loosely twisted plys or rovings 36 as shown in FIG. 6, each of which is comprised of a plurality of strands which in turn are comprised of a large number of continuous glass filaments. An alternative preferred structure of a fiberglass cord or cable 14a is shown in FIG. 6A wherein the plys or rovings 36:: are braided together. The braided structure provides for a greater variation in the cross sectional configuration and an increase in the surface irregularities along the length of the cable which in turn provides for an increase in the mechanical interlocking of the reinforcing network with the matrix of the abrasive article in which it is imbedded. The improved mechanical interlocking provided by these irregularities minimizes relative slippage between the reinforcing network and the structure of the grinding wheel providing for improved anchoring of any fractured segments of the wheel preventing their separation from the main body of the wheel. Alternative cable constructions can also be satisfactorily employed in which the several plys or rovings are intertwined in a manner so as to provide variations in the cross sectional configuration and irregularities in the surface of the cable.

Typically, the fiberglass cable usually contains from about 3 to about 6 plys or rovings 36 each of which is comprised of about 60 strands, for example, and each strand contains a large number of filaments such as about 200. The diameter of the individual fiberglass filaments used in making up the strands which in turn are twisted to form the fiberglass rovings or plys is not critical and can be manufactured by any of the conventional techniques well known in the art. It is only necessary that the filaments be of a sufliciently small diameter to enable bending the cable through a relatively small radius coinciding with the apexes of the cusps formed without cracking or otherwise impairing the strength of the glass filaments. The specific structure of the fiberglass cable or cord canbe varied in the number of fiberglass filaments employed, the number of strands employed, and the number of rovings or plys employed consistent with the cross sectional area desired to achieve the desired tensile strength.

It is conventional in the manufacture of fiberglass filaments to apply a suitable sizing finish to the surfaces of the filaments to facilitate subsequent handling thereof such as in spinning yarn and weaving fiberglass fabrics therefrom. The sizing material applied to the surfaces of the glass filaments acts as a lubricant during subsequent operations and concurrently prevents abrasion and fuzzing of the filaments. A variety of sizing materials are well known in the art which additionally increase the compatability between the fiberglass filaments and a variety of resins when the fiberglass is employed in the reinforced plastics art. For example, epoxy resin sizing finishes, phenolic resin sizing finishes, silane sizing finishes, and modifications of the foregoing are usually employed to increase the compatability of the fiberglass filaments to such plastics as polyesters, phenol aldehyde resins and epoxy resins. Accordingly, in the preferred practice of the present invention the fiberglass filaments are provided with a sizing on the surface thereof to increase the wettability and compatability of the fiberglass cord or cable with the bonding material employed in making the resinoid bonded abrasive article or with a resin impregnant employed to rigidify the reinforcing network as will be subsequently described.

By forming the reinforcing members so that approximately one-half of the chord elements thereof are tangent to an inner cylindrical surface or pass through a region within /3 of the radial depth of the wheel, the maximum stress and the maximum reinforcing characteristics of the reinforcing member will be disposed between the clamping flanges customarily employed in clamping and mounting the wheel on a rotating shaft. The diameter of the flanges customarily employed for mounting the wheel on a rotating shaft usually extends to about one-third the radial depth of the wheel. However, flange diameters are also employed which comprise, for example, from about to about of the radial depth of the wheel. For the purposes of the present invention, it is preferred that the chordal circle or region comprised of the plurality of chord segments be disposed in the grinding wheel at a point preferably not greater than the radial extension of the mounting flange diameters employed for clamping the grinding wheel to a rotating shaft. By this arrangement, the reinforcing effects of the mounting flanges and the chordal region are combined forming therewith a high strength assembly having its maximum reinforcement at the point of greatest stress.

The reinforcing members having the desired cuspate geometrical pattern can be conveniently formed by employing a forming jig 38 of the type shown in FIGS. 9 and 10. As shown in these figures the forming jig 38 is comprised of a base plate 40 including a plurality of pins 42 affixed thereto and projecting substantially perpendicular therefrom. The pins 42 are disposed in substantially equal angular increments of about 22 /2 along the circumference of a circle corresponding to the outer cylindrical surface or circle 20 of the reinforcing members. The pin arrangement shown enables the making of a cuspate geometrical pattern having a substantially regular configuration. The arcuate spacing of the pins 42 as well as their radial spacing from the center of the forming jig can be varied so as to achieve the desired configuration. As shown in FIG. 10 each of the pins 42 is provided with a plurality of height notches 44 which are disposed in equal linear spaced increments measured from the upper surface of the base plate 40.

A reinforcing member having a configuration corresponding to the cuspate geometrical pattern shown in FIG. 2 and of a substantially planar configuration is simply achieved by winding the continuous fiberglass cable 14 around the lowest height notch of the pins 42 until the completed pattern has been obtained in a manner as shown in FIGS. 9 and 10. After one complete reinforcing member has been wound, the cable 14 is wound to the same or other desired pattern on the pins 42 employing the second height notch. In this manner a plurality of interconnected layers or tiers of the reinforcing members are formed providing therewith a reinforcing network having the desired configuration and comprising the requisite number of layers. A nonplanar reinforcing member can similarly be wound by winding the cable around different height notches of different pins forming a network having the desired depth.

Since the reinforcing members made by employing the forming jig possess a degree of resiliency whereby upon removal from the forming jig the geometric cuspate pattern is somewhat distorted, it is usually preferred to impregnate the fiberglass cable with a suitable bonding agent prior to removal from the forming jig so as to rigidity the reinforcing network formed assuring shape retention after removal from the jig and facilitating the handling thereof during the manufacture of the reinforced abrasive article. Of equal importance is the prevention of relative slip between the fiberglass filaments assuring uniform loading thereof across a cross section of the cable. Rigidification of the fiberglass cable while wound on the forming jig can be achieved by any one of a number of suitable bonding materials such as partially cured phenol aldehyde resins and polyester resins, for example, of which phenol itself condensed with formaldehyde is the preferred resin. As hereinbefore set forth, a sizing finish on the surface of the fiberglass such as epoxy silanes or modified silanes compatible with the bonding agent is preferred to improve the wettability and impregnatability of the bonding resin. The bonding agent can be applied to the fiberglass cable network while on the forming jig by any one of a variety of techniques such as spraying, brushing, and dipping, for example. One convenient method has been found comprising inverting the forming jig having the fiberglass cable wound therearound and immersing the fiberglass cables in a suitable resin solvent solution whereby the individual strands and fiberglass rovings comprising the fiberglass cable are wetted and which on subsequent curing forms a rigidified reinforcing network. Application of the bonding agent can also be done prior to winding the cable in the desired pattern.

A reinforcing network comprising the desired number of reinforcing members each having the desired cuspate geometrical configuration can be conveniently incorporated within the body of an abrasive article by any one of a number of techniques well known in the art such as cold pressing, hot pressing, and preferably by one of the displacement methods as set forth in United States Patent No. 2,860,961 and assigned to the same assignee as the present invention. The displacement methods as set forth in the aforementioned patent have the advantage of not requiring excessive pressures for forming the preliminary abrasive article. In comparison, relatively high pressures are necessary in conventional cold pressing and hot pressing operations which subject the fiberglass reinforcing network to possible damage by imbedding the abrasive particles therein thereby impairing the resultant strength of the reinforcing network. Additionally, high pressures also cause damage to the abrasive grains.

Regardless of the specific method employed for making the resinoid bonded article incorporating the fiberglass reinforcing network therein, the abrasive article should generally contain from about 40% to about 64% by volume of a suitable abrasive and from about 36% to about 60% by volume of the bonding material including various amounts of binder resin, fillers, plasticizers, the reinforcing network, pores and other additives. The reinforcing effectiveness of the fiberglass reinforcing network is obtained in abrasive articles made from any one or mixtures of abrasive grains, binder resins, fillers, etc., conventionally employed. Abrasive articles of the general type to which the present invention is applicable can include such conventional abrasive grains as silicon carbide, boron carbide, tantalum carbide, tungstencarbide, or other hard metal carbides; alumina such as emery and including electric furnace fused alumina such as corundum, diamond grains, glass, quartz, garnet, etc. In addition, any of the conventional filler materials such as powdered cryolite, feldspar, iron oxide and others which are inert or which improve cutting eificiency can be employed satisfactorily. If desired, the bond compositions may also contain lime and where furfuraldehyde is employed, the presence of lime is recommended.

In addition to the abrasive grains and the filler materials any one of a variety of the conventional resin binders can be employed for binding the abrasive particles together forming therewith an integral resinoid bonded abrasive article. Conventional binder resins employed for forming resinoid bonded articles are of the thermosetting type which are heat hardenable or heat convertible into a hard, strong bond. Binding resins which can be satisfactorily employed are well known in the art and include the phenol aldehyde resins, cresol aldehyde resins, resorcinol aldehyde resins, urea aldehyde resins, melamine formaldehyde resins, fufuryl alcohol resins, and the like, as well as various mixtures thereof. Of the various binding resins available the condensation product of phenol itself with formaldehyde constitutes the preferred binding resin.

As hereinbefore stated, the displacement method constitutes the preferred method of making the reinforced abrasive articles incorporating the fiber glass cuspate geometrical reinforcing network. However, satisfactory reinforced abrasive articles can also be made by the conventional cold pressing and hot pressing methods well known in the art. In the cold pressing method for eX- ample, a quantity of abrasive particles or grains are substantially uniformly coated with a suitable binder resin such as an A-stage phenolic resin for example, either in powdered or liquid form which may include in addition a desired quantity of filler materials, plasticizer, etc. To facilitate coating of the abrasive grains, it has been found that by preliminary wetting the surfaces of the abrasive grains with a solvent for the phenolic resin such as furfural, for example, and thereafter adding the powdered phenolic resin substantially uniform coating of the abrasive grains is obtained.

A variety of other techniques for providing a substantially uniform coating of the abrasive grains with the desired proportion of a suitable binder resin can be employed and the resultant coated abrasive mixture can be placed in a suitable mold. A fiberglass reinforcing network having a configuration of the desired form and comprising from about .2% to about 2% by weight of the resultant article is placed in the mold and surrounded by the coated abrasive grain mixture. Thereafter the abrasive mixture having the reinforcing network imbedded therein is cold pressed under high pressures such as, for example, at about at least 2 or 3 tons per square inch after which the preliminary formed abrasive article is heated to an elevated temperature to cure the resin bonding agent forming therewith an integral structure. Alternatively, the uniformly coated abrasive mixture and/ or the mold can be heated to an elevated temperature providing therewith a hot pressing action in which partial curing of the resin is accomplished in the mold followed thereafter by a final curing step.

The displacement methods disclosed in the aforementioned patent for making abrasive articles are preferred not only because of avoidance of injury to the fiberglass reinforcing network imbedded therein during the forming process, but additionally because of avoidance of damage to the abrasive grains themselves incurred during the pressing operation and the greater density, less voids, and higher grinding efiiciency obtained from the resultant abrasive article. In accordance with the practice of the displacement methods as disclosed in the aforementioned patent a differential pressure is employed to cause the penetration of a preliminarily mixed bonding material through a body of dry abrasive grains disposed in a mold of a desired shape and whereby the bonding material substantially completely fills the pores in the abrasive grain body displacing substantially all of the air therefrom after which the penetrated abrasive grain body is cured at an elevated temperature forming a resinoid bonded abrasive article.

The method by which the differential pressure is created to cause substantially complete penetration and filing of the abrasive grain layer in a directional manner can include the utilization of a pressure differential across the layer of bond material and abrasive grains, or by utilizing centrifugal force. The pressure differential across the layers can be created by applying a vacuum to the side of the abrasive grain layer opposite to the bond material or by applying a positive pressure over the bonding material to force it through the abrasive layer toward the opposite surface thereof. The force of gravity can similarly be employed but is more time consuming.

Penetration achieved by the action of centrifugal force can be achieved by employing a spinning mold or one which is swung on gimbals as shown in the aforementioned patent whereby directional movement of the penetrating bonding material is achieved from one surface to the opposite surface thereof. In any one of these displacement methods a barrier layer is employed which prevents leaking through of the bonding material after it has completed penetration and reaches the opposite surface of the abrasive grain layer.

A specific example of one of the displacement methods disclosed in the aforementioned patent is illustrated in FIGS. 7 to 8 wherein vacuum is employed to cause a differential pressure across the abrasive grain layer causing the bonding material to flow therethrough and substantially completely filling the voids thereof. As shown in the drawings, a mold assembly suitable for applying a vacuum across an abrasive grain layer to assist the displacement movement of the bonding material through the voids therein is comprised of a base plate 46 having a vacuum chamber 48 which is provided with a suction tube 50. A foraminous top plate 52 is securely fastened to the base plate 46 employing a gasket 54 therebetween forming therewith an air-tight seal. A circular, split band outer mold member 56 is disposed on the upper surface of the top plate 52 and is provided with a pair of outwardly projecting flaps 58 which can be secured by bolts to form a continuous circle. The outer mold member 56 can be made of light weight fairly flexible sheet metal since it is not subjected to high pressures in use.

The mating surfaces between the top plate 52 and outer mold member 56 are preferably provided with a suitable O-ring 60 to form a vacuum type seal therebetween. Appropriate alignment and positioning of the outer mold member 56 with respect to the top plate 52 is achieved by a series of abutments 62 afiixed to and projecting from the top plate. An upstanding core 64 is disposed on the top plate 52 concentric with the outer mold member 56 and forms the hole through the abrasive wheel. The core 64 can be permanently anchored to the top plate 52 or can be removable therefrom. Alternatively, the core 64 could be an arbor intended to be permanently molded in the Wheel or can be reusable and be provided with an overlying fiber layer or collar 66 to prevent adhesion of the bond material to the core.

To effect communication between the vacuum chamber 48 and the annular cylindrical area between the outer mold member 56 and core 64, the top plate 52 is provided with a plurality of fine holes 68. A retainer ring 70 of a fairly coarse wire construction, for example is placed on top of the fine holes 68 over which a barrier ring 72 is placed which is pervious to air but which is substantially impervious to or which will resist penetration by the bonding material. Barrier rings comprised of such material as cardboard chip stock, filter paper, and the like can be satisfactorily employed.

As shown in FIG. 7, a relatively thin layer of a dry abrasive grain mixture 74 is placed directly over the barrier ring 72 and on which abrasive grain mixture the fiberglass reinforcing network 26 of the desired configuration and quantity is positioned so that the apexes of the network are substantially concentric with the outer mold member 56. Additional abrasive particles are thereafter added in the mold until the reinforcing network 26 is completely imbedded therein. The abrasive particles can be tamped in the mold or alternatively the entire mold assembly can be vibrated to cause substantially complete filling of the spaces between the fiberglass cables 14 of the reinforcing network forming therewith an abrasive layer 76 as shown in FIG. 8 of the desired height. A preliminarily mixed bonding mixture 78 of the desired composition is then applied directly over the top of the abrasive layer 76 forming a continuous layer. Thereafter vacuum is applied to the vacuum chamber 48 whereby the bonding mixture 78 is sucked downwardly through the channels between the abrasive grains of the abrasive layer 76 and during which penetration the air is displaced from the voids of the abrasive layer and is drawn through the barrier ring 72 through the holes 68 and out through the suction tube 50.

To achieve satisfactory penetration of the abrasive layer 76 the viscosity of the bonding mixture is of some importance since the material should form a continuous layer and be capable of flow when applied to the grains. It has been found that the maximum viscosity which can be conveniently formed into such layer and which can be caused to penetrate an abrasive layer in a reasonable time is about 20,000 centipoises (cps). The minimum viscosity which can be handled is about 500 cps. When solid powdered resin binders are employed, the bonding mixture should have a viscosity not appreciably higher than that obtained when about 200 ml. of furfural, or its equivalent, is admixed with one pound of a typical powdered A-stage phenol formaldehyde resin. The bond ing mixture can be applied at about room temperature to a mold which likewise is at about room temperature or alternatively the mold and abrasive layer therein can be preliminarily heated to a temperature ranging from about room temperature (i.e., about 80 F.) to about 350 F. Similarly, the bonding mixture itself can also be preheated prior to application over the abrasive layer 76 to a temperature ranging from about 130 to about 260 F. and preferably in the range from about 165 F. to about 220 F.

The resinous materials suitable for forming the bonding mixture include those which can be employed in the cold pressing and hot pressing methods for making resinoid bonded abrasive articles as hereinabove set forth. Similarly, phenol formaldehyde condensation products of the standard Bakelite type in powdered or liquid form have been found to be unusually satisfactory when employed in the displacement method. If desired, the phenol aldehyde resins can be modified with small quantities of other resinous materials such as epoxy resins, vinyl resins including vinyl chloride, vinyl butyral, vinyl formal, vinyl acetate and others and may contain varying percentages of cross-linking aids such as hexamethylene tetramine or paraformaldehyde, and suitable solvents or plasticizers such as furfuraldehyde and propylene sulfite. Other plasticizers such as cresol, furfuryl alcohol, or the like may be employed if desired.

As an illustrative example of an abrasive article made by the displacement method, the article can contain from about 40% to about 65% by volume of a suitable abrasive grain, from about 16% to about 26% by volume of a bonding resin or resins such as phenol formaldehyde, for example, from about 1% to about 4% by volume of lime, from about 8% to about 35% of a filler such as cryolite, for example, and from about 0 to about 200 ml. of furfuraldehyde for each pound of powdered phenol aldehyde resin employed. In addition, small quantities of hexamethylene tetramine, paraformaldehyde, and other auxiliary cross linking agents or hardeners may be employed.

A particularly satisfactory set of conditions which are suitable for the manufacture of abrasive grinding wheels by the displacement method is to heat the bonding material to a temperature below that at which it will cure rapidly, for example, from F. to about 180 F. for a bonding mixture containing hexamethylene tetramine hardener, heating the abrasive grain mixture and the mold to a temperature well above the curing temperature of the resinous bonding mixture, for example, from about 200 F. to about 350 F., rapidly applying a layer of the bonding mixture to the abrasive grain layer and forcing it down through the voids thereof. The high tempera- .ture of the abrasive grains momentarily produces a higher fluidity in the applied bonding layer which enables its ready penetration and more uniform filling of the pores and the irregularities in the surface of the fiberglass reinforcing network imbedded therein, but shortly after the pores and irregularities are filled the bonding material starts to thicken and harden due to cure and this hardening provides early rigidity in the resinoid bond and freedom from flow to permit removal of the resultant abrasive article from the mold. The abrasive article thus made can thereafter be placed in an oven at an elevated temperature if necessary, to complete the cure of the bonding material therein.

When penetration of the bonding material into the abrasive grain layer is achieved at room temperature relatively little curing of the bonding material occurs during the penetrating movement thereof. Accordingly, after penetration is complete the vacuum is broken and the mold assembly and its contents are placed in an oven at an elevated temperature to achieve curing and tenacious bonding of the abrasive particles and the reinforcing network therein to the bonding material.

The resultant cured wheel can thereafter be removed from the mold and any excess bonding material on the surfaces thereof can be removed by dressing the wheel.

The specific steps described in connection with the vacuum molding displacement method as shown in FIGS. 7 and 8 can similarly be employed for displacement methods of the pressure type and of the centrifugal force type as described in detail in the aforementioned patent to which reference is made for a more detailed description of the various displacement techniques.

The effectiveness of the fiberglass reinforcing network for strengthening relatively large heavy duty grinding wheels will now be illustrated in greater detail based on destructive tests conducted on a series of grinding wheels employing the same abrasive grain structure and bonding material and deviating in the specific quantity and configuration of the reinforcing network employed. Data are provided enabling a comparison of the strength of a number of grinding wheels employing reinforcing networks of the geometrical cuspate patterns hereinabove shown and described in comparison to grinding wheels embodying conventional steel reinforcing rings.

The test grinding wheels in each of the following examples employed an abrasive grain mixture comprising Nos. 10, 12, 14, and 16 aluminum oxide abrasive grains which comprised about 60% of the volume of the test wheel. Each of the test wheels were made by employing the vacuum displacement technique of the type employing a mold similar to that shown in FIGS. 7 and 8 wherein the abrasive grain mixture was placed in the mold employing a barrier ring comprising a cardboard chip stock material positioned on a screen type barrier retainer ring 70. The reinforcing network was imbedded in the abrasive grains and the bonding layer was thereafter applied.

The specific composition of the bonding material employed in making the test samples is tabulated below:

BONDING MATERIAL Ingredient: Volume percent Powdered A-stage phenolic resin (Varcum 3025) 44.9 Powdered potassium sulfate 14.0 Zinc sulfide 6.0 Lime 7.3

Geon 202 (copolyrner of polyvinyl chloride and polyvinylidene chloride) 8.0 Furfural 19.8

The above bonding mixture was employed in a quantity so as to constitute about 40% by volume of the abrasive grain structure of the test grinding Wheels.

Prior to applying the bonding mixture to the upper surface of the abrasive grain layer in the mold, the mold and abrasive grain mixture were heated to a temperature of 250 F. and the bond mixture was heated to a temperature of 160 F. At these temperatures the bonding mixture was applied to the upper surface of the abrasive layer in the mold and the vacuum was applied forcing quick and substantially complete penetration of the bonding material through the abrasive grain layer. The mold thereafter was permitted to stand for an hour or more in an oven at 250 F. allowing for partial curing of the bonding material in the abrasive grain layer and was thereafter removed from the mold and placed in an oven at an elevated temperature to cause substantially complete and final curing of each of the test Wheels.

In each of the sample test wheels made employing a fiberglass reinforcing network, the continuous fiberglass cord was disposed in a substantially planar cuspate geometrical pattern corresponding to that of FIG. 2 having an outer diameter as measured on the outer circle 20 of 23 inches and a chordal ring having a diameter as measured on the inner circle 21 of 13 inches.

Employing the abrasive grain mixture, the bonding material composition, and vacuum molding technique as set forth above, the following sample test grinding wheels were made:

Example I Three test wheels having an outer diameter of 24 inches, an inner diameter of 12 inches and a thickness of 3 inches were made employing standard reinforcing techniques consisting of two 14 inch outer diameter rings of steel wire having a inch diameter cross section and having the connecting ends thereof butt welded. These standard test wheels are designated as samples A, B, and C. The two steel reinforcing rings were placed in the abrasive grain mixture prior to the application of the bonding material and were disposed in side by side spaced 16 relationship concentrically with the inner bore diameter of the grinding wheel.

Example II Three grinding wheels were prepared having an outer diameter of 24 inches, an inner bore diameter of 12 inches and a thickness of 3 inches. These grinding wheels are designated as samples D, E, and F. Each of the grinding wheels incorporated five interconnected reinforcing members having a cuspate geometrical pattern corresponding to that shown in FIG. 2 of the drawings. The continuous fiberglass cord or cable employed in the reinforcing network of sample D had three fiberglass rovings whereas the reinforcing networks of samples E and F incorporated six fiberglass rovings. Each fiberglass roving comprised 60 strands and each strand was comprised of 204 continuous filaments of glass. The rovings were obtained from Owens-Corning Fiberglas Corporation and are designated as 60E 801 epox C. As indicated, the fiberglass fiaments had a sizing finish on the surfaces thereof of an epoxy resin. The reinforcing members were wound on a forming jig of the type shown in FIGURES 9 and 10 and in that form were placed in the annular mold cavity and imbedded in the abrasive material. Thereafter the network was removed from the pins and the forming jig was withdrawn and the mold vibrated to assure complete filling of the voids around the reinforcing members. The bonding material was thereafter applied and cured in a manner as set forth above.

Example III Two test grinding wheels designated as samples G and H were made having an outside diameter of 24 inches, an inside diameter of 12 inches and a thickness of 3 inches and employing five reinforcing members of the type shown in FIG. 2 of the drawings and in which the fiberglass cord or cable comprised 6 rovings of the same type as used in Example II. The reinforcing networks were preliminarily treated and rigidified prior to placement in the mold by dipping the forming jig in a solution containing 50% by volume of a liquid phenolic resin supplied by the Union Carbide Plastics Company and designated BRL-2534 and 50% by weight methanol. After the fiberglass filaments in the contiuous fiberglass cable were thoroughly impregnated with the resin solution, the forming jig was placed in an oven at a temperature of 250 F. for a period of about three hours to cure the phenolic resin forming a rigidified reinforcing network. Thereafter, the reinforcing network was placed concentrically in the mold cavity in a manner as shown in FIG. 7 and imbedded in the abrasive grain after which the bonding material was applied and penetrated throughout the abrasive grain mixture.

Example I V Three test grinding wheels were made having an outer diameter of 24 inches, an inner diameter of 12 inches, and a thickness of 2 /2 inches. These grinding wheels are designated as samples I, J, and K. Test wheel samples I and J incorporated four interconnected reinforcing members having a configuration as shown in FIG. 2 made of a reinforcing cable comprising 6 loosely twisted fiberglass rovings of the same type as employed in Example II and which networks were pretreated and rigidified by dipping in a resin solution in the manner as described in Example III. The reinforcing network employed in sample K was similar to that of samples I and J except that five reinforcing members were employed instead of four.

Sample test wheels A, B, D, E, F, G, I, J, and K made in accordance with the steps as outlined in the examples above, were subjected to a so-called Breaking Test after they were cracked across their diameters by placing them in a press and were thereafter speeded to destruction. In this way the breaking of a wheel or disintegration thereof is established exclusively by the strength of the reinforcing network since the diarnetral crack across the wheel eliminates the contributing strength of the abrasive grain structure against rupture or breakage of the wheel. In addition, the test wheels compris ing samples C' and H were subjected to a so-called shot test wherein the wheels were shot with 3006 caliber armor piercing bullets and then speeded to destruction. The following table contains data. relating to the rotative speed of the grinding Wheels at which breaking or disintegration occurred and is expressed in terms of surface feet per minute (s.f.p.m.)':

DESTRUCTIVE TEST DATA Breaking Speed, s.f.p.m.

Test Wheel Sample Breaking Shot Test Test A (Standard, 11,400 13 (Qtandard) 12, 700

It is apparent from the test data obtained that higher breaking speeds were obtained for the test wheels incorporating the fiberglass reinforcing network than Was obtained for the standard test wheels incorporating the steel rings. This is particularly true of the shot test wherein sample H had a breaking speed of more than 10,000 s.f.p.m. greater than the standard test wheel represented by sample C.

A comparison of the breaking speed of samples D and E indicates that by incorporating six rovings in the fiberglass cable instead of three causes a significant improvement in the strength of the reinforcing network. In addition, a comparison between the breaking speed obtained on samples F and G substantiates the superiority in the reinforcing network when subjected to preliminary treatment comprising rigidification by a binding resin such as the liquid phenolic resin described in the example. The breaking speeds obtained on the test wheel samples I, J, and K, which had a thickness of /2 inch less than the other test Wheels indicated extremely high strength of the pretreated fiberglass reinforcing network therein. An improvement of over 1,000 s.f.p.m. was obtained in sample K over that of samples I and J by incorporating five reinforcing members instead of only four reinforcing members.

In each case the breaking speed of the test wheels incorporating the fiberglass reinforcing network in accordance with the preferred embodiments of the present invention were substantially in excess of the operating conditions to which the wheels are conventionally subjected to in commercial use. Generally, commercial operating speeds are in the order of about 9,500 s.f.p.m. which is substantially below the breaking speed obtained on the test wheels. It will of course be appreciated that the breaking speeds of the test wheels would be even higher had they not been cracked across the diameter.

While it will be apparent that the preferred embodiments herein illustrated are well calculated to fulfill the objects above stated, it will be appreciated that the invention is susceptible to modification, variation, and change without departing from the proper scope or fair meaning of the subjoined claims.

What is claimed is:

1. A reinforcing network for strengthening rotating articles subjected to centrifugal forces such as grinding wheels and the like, said reinforcing network comprising at least one reinforcing member comprising a continuous fiberglass cord positioned in a cuspate geometrical pattern and disposed in an annular region defined by an inner cylindrical surface and an outer cylindrical surface disposed in concentric axial alignment to each other, said pattern comprising a plurality of radially projecting cusps having the apexes thereof lying on the outer cylindrical surface and disposed in substantially equal angular increments therealong, said cusps formed by a plurality of pairs of chord elements lying in the annular region and extending between two points on the outer cylindrical surface and intersecting substantially equal arcuate segments thereof, at least about half of said chord elements passing through an inner chordal region which lies between the inner cylindrical. surface and an intermediate cylindrical surface concentric to the inner cylindrical surface and spaced outwardly therefrom a distance of about one-third the radial depth of the annular region, said reinforcing member further characterized as having a distribution of said continuous fiberglass cord wherein the volume of said cord increases in the direction from the outer cylindrical surface to the chordal region.

2. A. reinforcing network for strengthening rotating articles subjected to centrifugal forces such as grinding wheels and the like, said reinforcing network comprising at least one reinforcing member comprising a continuous fiberglass cord positioned in a cuspate geometrical pat.- tern and disposed in an annular region defined by an inner cylindrical surface and an outer cylindrical surface disposed in concentric axial alignment to each other, said pattern comprising a plurality of radially projecting cusps having the apexes thereof lying on the outer cylindrical surface and disposed therealong in substantially equal angular increments, said cusps formed by a plurality of pairs of chord elements lying in the annular region and extending between two points on the outer cylindrical surface and intersecting substantially equal arcuate increments thereof, said chord elements disposed tangent to the inner cylindrical surface, said chord elements disposed in substantially the same plane imparting a substantially pianar configuration to said reinforcing member, said pattern further characterized as having a distribution of said continuous fiberglass cord wherein the volume of said cord increases in the direction from the outer cylindrical surface to the inner cylindrical surface.

3. A reinforcing network for strengthening rotating articles subjected to centrifugal forces such as grinding wheels and the like, said reinforcing network comprising at least one reinforcing member comprising a continuous fiberglass cord positioned in a cuspate geometrical pattern and disposed in an annular region defined by an inner cylindrical surface and an outer cylindrical surface disposed in concentric axial alignment to each other, said pattern comprising a plurality of radially projecting cusps formed by a plurality of pairs of chord elements lying in the annular region, at least about half of said chord elements passing through an inner chordal region which lies between the inner cylindrical surface and an intermediate cylindrical surface concentric to the inner cylindrical surface and spaced outwardly therefrom a distance of about one-third the radial depth of the annular region, said reinforcing member further characterized as having a distribution of said continuous cord wherein the volume of said cord increases in the direction from the outer cylindrical surface to the chordal region, said continuous fiberglass cord comprising a plurality of braided fiberglass rovings each of which comprises a plurality of fine sized continuous fiberglass filaments.

4. A reinforced abrasive article adapted to rotate at relatively high speeds about an axis of rotation such as a grinding wheel and the like, said abrasive article comprising abrasive grains, a resinous bonding material, and a reinforcing network imbedded in the body of said article, said reinforcing network comprising at least one reinforcing member comprising a continuous fiberglass cord positioned in a cuspate geometrical pattern and disposed in an annular region defined by an inner cylindrical surface and an outer cylindrical surface concentric to the 3% axis of rotation of said article, the outer cylindrical surface lying in the region extending from the periphery of said article to a point spaced inwardly from the periphery a distance of about one-third the radial depth of the annular region, said pattern comprising a plurality of radially projecting cusps formed by a plurality of pairs of chord elements lying in the annular region, at least about half of said chord elements passing through an inner chordal region which lies between the inner cylindrical surface and an intermediate cylindrical surface concentric to the inner cylindrical surface and spaced outwardly therefrom a distance of about one-third the radial depth of the annular region, said reinforcing member further characterized as having a distribution of said continuous fiberglass cord wherein the volume of said cord per unit volume of said article increases in the direction from the outer cylindrical surface to the chordal region.

5. A reinforced abrasive wheel having a bore or arbor extending axially through the center thereof for rotatably mounting said wheel, said wheel comprising abrasive grains, a resinous bonding material, and a reinforcing network imbedded in the body of said wheel, said reinforcing network comprising a plurality of interconnected reinforcing members disposed in side by side relationship and comprising a continuous fiberglass cord, said cord of each of said reinforcing members positioned in a cuspate geometrical pattern and disposed in an annular region defined by an inner cylindrical surface and an outer cylindrical surface concentric to the bore or arbor through said wheel, the outer cylindrical surface lying in the region extending from the periphery of said wheel to a point spaced inwardly from the periphery a distance of about one-third the radial depth of said wheel and the inner cylindrical surface having a diameter corresponding to the bore or arbor of said wheel, said pattern comprising a plurality of radially projecting cusps formed by a plurality of pairs of chord elements lying in the annular region, at least about half of said chord elements passing through an inner chordal region which lies between the inner cylindrical surface and an intermediate cylindrical surface concentric to the inner cylindrical surface and spaced outwardly therefrom a distance of about one-third the radial depth of said wheel, said reinforcing member further characterized as having a distribution of said continuous fiberglass cord wherein the volume of said cord per volume of said wheel increases in the direction from the periphery of said wheel to the chordal region.

6. A reinforced abrasive wheel having a bore or arbor extending axially through the center thereof for rotatably mounting said wheel, said wheel comprising abrasive grains, a resinous bonding material, and a reinforcing network imbedded in the body of said wheel, said reinforcing network comprising at least one reinforcing member comprising a continuous fiberglass cord positioned in a cuspate geometrical pattern and disposed in an annular region defined by an inner cylindrical surface and an outer cylindrical surface concentric to the bore or arbor through said wheel, the outer cylindrical surface lying in the region extending from the periphery of said wheel to a point spaced inwardly from the periphery a distance of about one-third of the radial depth of said wheel and the inner cylindrical surface having a diameter corresponding to the bore or arbor through said wheel, said pattern comprising a plurality of radially projecting cusps having the apexes thereof lying on the outer cylindrical surface and disposed in substantially equal angular increments therealong, said cusps formed by a plurality of pairs of chord elements lying in the annular region and extending between two points on the outer cylindrical surface and intersecting substantially equal arcuate segments thereof, at least about half of said chord elements passing through an inner chordal region which lies between the inner cylindrical surface and an intermediate cylindrical surface concentric to the inner cylindrical surface and spaced outwardly therefrom a distance of about one-third the radial depth of said wheel, said pattern further characterized as having a distribution of said continuous fiberglass cords wherein the volume of said cord per unit volume of said wheel increases in the direction from the periphery of said wheel to the chordal region.

7. A reinforced abrasive wheel having a bore or arbor extending axially through the center thereof for rotatably mounting said wheel, said wheel comprising abrasive grains, a resinous bonding material, and a reinforcing network imbedded in the body of said wheel, said reinforcing network comprising at least one reinforcing member comprising a continuous fiberglass cord positioned in a cuspate geometrical pattern and disposed in an annular region defined by an inner cylindrical surface and an outer cylindrical surface concentric to the bore or arbor through said wheel, the outer cylindrical surface lying in the region extending from the periphery of said wheel to a point spaced inwardly from the periphery a distance of about one-third the radial depth of said wheel, the inner cylindrical surface disposed concentric to the bore or arbor through said wheel and disposed in a chordal region extending from the bore or arbor outwardly a distance of about one-third the radial depth of said wheel, said pattern comprising a plurality of radially projecting cusps having the apexes thereof lying on the outer cylindrical surface and disposed therealong in substantially equal angular increments, said cusps formed by a plurality of pairs of chord elements lying in the annular region and extending between two points on the outer cylindrical surface and intersecting substantially equal arcuate increments thereof, each of said chord elements disposed tangent to the inner cylindrical surface, said chord elements disposed in substantially the same plane imparting a substantially planar configuration to said reinforcing member, said reinforcing member further characterized as having a distribution of said continuous fiberglass cord wherein the volume of said cord per unit volume of said wheel increases in the direction from the periphery of said wheel to the inner cylindrical surface.

8. A reinforced abrasive wheel as described in claim 7 wherein said reinforcing network comprises a plurality of said reinforcing members disposed in side by side relationship and interconnected by said continuous fiberglass cord.

9. A reinforced abrasive wheel as described in claim 7 wherein said continuous fiberglass cord comprises a plurality of braided fiberglass rovings each of which comprises a plurality of fine sized continuous fiberglass filaments.

10. A reinforced abrasive wheel as described in claim 9 wherein said fiberglass filaments comprising said rovings are tenaciously bonded together by a bonding agent impregnated in said fiberglass cord forming therewith a rigiditied reinforcing network.

11. A reinforced abrasive wheel as described in claim 10 wherein said bonding agent comprises a thermosetting phenol aldehyde resin and wherein the surfaces of said continuous fiberglass filaments are provided with a sizing compatible with said bonding agent.

References Cited in the file of this patent UNITED STATES PATENTS 1,537,790 Alpe May 12, 1925 1,638,012 Hoof Aug. 9, 1927 2,282,717 Frieder May 12, 1942 2,350,504 Feier et al June 6, 1944 2,763,105 Feeley Sept. 18, 1956 2,826,016 Hurst Mar. 11, 1958 

1. A REINFORCING NETWORK FOR STRENGTHENING ROTATING ARTICLES SUBJECTED TO CENTRIFUGAL FORCES SUCH AS GRINDING WHEELS AND THE LIKE, SAID REINFORCING NETWORK COMPRISING AT LEAST ONE REINFORCING MEMBER COMPRISING A CONTINOUS FIBERGLASS CORD POSITIONED IN A CUSPATE GEOMETRICAL PATTERN AND DISPOSED IN AN ANNULAR REGION DEFINED BY AN INNER CYLINDRICAL SURFACE AND AN OUTER CYLINDRICAL SURFACE DISPOSED IN CONCENTRIC AXIAL ALIGNMENT TO EACH OTHER, SAID PATTERN COMPRISING A PLURALITY OF RADIALLY PROJECTING CUSPS HAVING THE APEXES THEREOF LYING ON THE OUTER CYLINDRICAL SURFACE AND DISPOSED IN SUBSTANTIALY EQUAL ANGULAR INCREMENTS THEREALONG, SAID CUSPS FORMED BY A PLURALITY OF PAIRS OF CHORD ELEMENTS LYING IN THE ANNULAR REGION AND EXTENDING BETWEEN TWO POINTS ON THE OUTER CYLINDRICAL SURFACE AND INTERSECTING SUBSTANTIALLY EQUAL ARCUATE SEGMENTS THEREOF, AT LEAST ABOUT HALF OF SAID CHORD ELEMENTS PASSING THROUGH AN INNER CHORDAL REGION WHICH LIES BETWEEN THE INNER CYLINDRICAL SURFACE ANDAN INTERMEDIATE CYLINDRICAL SURFACE CONCENTRIC TO THE INNER CYLINDRICAL SURFACE AND SPACED OUTWARDLY THEREFROM A DISTANCE OF ABOUT ONE-THIRD THE RADIAL DEPTH OF THE ANNULAR REGION, SAID REINFORCING MEMBER FURTHER CHARACTERIZED AS HAVING A DISTRIBUTION OF SAID CONTINOUS FIBERGLASS CORD WHEREIN THE VOLUME OF SAID CORD INCREASES IN THE DIRECTION FROM THE OUTER CYLINDRICAL SURFACE TO THE CHORDAL REGION. 